Communicating system for power-transmission lines



Aug. 13, 1929. M. SINDEBAND ET AL 1,724,112

COMMUNICATING SYSTEM FOR POWER TRANSMISSION LINES Filed Jan. 28 1920' 5 Sheets-Sheet 1 A a a Q Q is Aug. 3, 1929. M. L. SINDEBIAND ET'AL 1,724,112

COMMUNICATING SYSTEM FOR POWER TRANSMISSION LINES File c1 Jan. 28- 1920 3 Sheets-Sheet 2 41 5& 4W E F 317? zz S I 1 I 2 g E L j 5 '1 g 1/ H LL 3a 1 VFW, I 6L3 E VVVVVU g- 1929. M. L. SINDEBIAND ET AL 1,724,112

COMMUNICATING SYSTEM FOR POWER TRANSMISSION LINES Filed Jan. 28- 9 3 Sheets-Sheet 5 Patented Aug.'1'3, 1929.

UNITED STATES PATENT OFFICE.

MAURICE L. SINDERBAND, OF NEW YORK, N. Y., GEORGE N. TIDD, 0F ELIZABETH,

NEW .masEY, AND JOSEPH w. MILNOR, mar. ELECTRIC COMPANY, a aoarona OF NEW YORK, N. Y., ASSIGNORS TO 01m- TION OF NEW YORK.

OOHUNIGATING SYSTEM FOR POWER-TRANSMISSION LINES.

Application filed January 28, 1920, Serial No. 354,602. Renewed December 18, 1928.

This invention relates to systems for conveying intelligence. More specifically it relates to systems for telephoning or telegraphing over a line employed to transmit power.

Alternatingcurrent transmission lines have long since been employed, and are coming into more general use, to transmit power to points distant fronrthe source of power. In order properly to ofirateihese systems and to render them efiective 1t is desirable that some form of reliable, private, communicating system, such as the telephone or telegraph, be provided between the power supply station and the consuming station or stations. The desirability or necessity for such a communication is emphasized by the now common interchange contracts entered into between various companies operating plants and interconnected transmission lines. In the past it has been the practice to install telephone or telegraph Wires on the same poles or towers which support the hightension power wires or conductors. This method is open to objection because of the cost of the signal line wire. But a still greater objection exists due to the inductive disturbances set up in the signaling conductors due to the proximity of the power conductors. The last mentioned objection may be more or less over- I come by mounting the signaling conductors on separate poles spaced from those which support the power lines. However, this method increases the installation and maintenance costs still more.

One of the. principal objects of the present invention is to provide a novel form of land line, signaling or communicating system in which no line wires other than the power transmission conductors are required and in which there is tactically no disturbance, inductive or ot erwise, between the power transmitting and signalling systems. Other objects and advantages will appear as the invention is hereinafter disclosed.

Referring to the drawings which illustrate what we now consider preferred forms of our invention:

Fig. 1 is a diagrammatic-view illustrating one form of telegraph system embodying our invention.

Fig. 9 is a modified form of telegraph system.

Fig. 10 is a diagram utilized in explaining the'theory of operation of the system shown in Fi 9.

Fig. 11 illustrates diagramatieally, a form of transmitting means, diflerent from that in Fig. 3, for su rimposin upon the transmission line a requency t ree' times that of the power current. V

Fig. 12 is a diagram employed in explaining the theory of operation. of the means shown in Fig. 11.

Fig. 13 illustrates a system somewhat similar to that in Fig. 1, but slightly modified.

While the invention it applicable to an alternating current transmissionline of any number of phases we have shown it applied to a three-phase system. In Fig. 1 the power is adapted to be supplied to the line throu h the conductors 1 (supplied by a suitab e generator, not shown) and a stepup transformer T. The rimaryand secondary of the latter are connected and the threebase, three-wire line is indicated at 151 l. The other end of the line is hown connected to the primary of a step-dd\wn transformer T, the secondary of which 's connected to lines 2 th shown delta which go to the load. The system thus far the line Z-Z". For example, if the power frequency is 60 cycles per second the frequency of the generator Cr may be 400 cycles. The generator G is shown connected to and controlled by a key K and coupled to one phase Z of the line by means of a current transformer of whiclrone winding is designated C. Obviously, with the switch 3 in the positionshown at station S, depression of the key K will cause the generator Gr to supply current to the transmission line at a frequency equal to that for which said generator is designed, or in the example above, 400 cycles. In order substantially to prevent the power current (assumed to be at 60 cycles) from reacting on the circuit G, K, the means shown at 4, 5 in Fig. 1

may be employed. It will be seen that the inductance 4 and capacity 5 are connected in parallel across the winding 0 and these impedances are designed or adjusted for parallel resonance; i. e., to be antiresonant, at the frequency of the generator- G. This means that with the values of frequencies above assumed the combined impedance offered to the signal current at 100 cycles by the elements 4, 5 will be practically infinite although the impedance offered by the last mentioned elements to the passage of the power current will be comparatively low. This means that so far as the passage of signaling current in' the circuit G, K, C is concerned the set 4-5 is substantially of no effect. On the other hand, practically all of the lower frequency current, introduced into the local circuit by the winding C, passes through the elements 45 by virtue of the comparatively low impedance of the latter at the power frequency.

The receiving means at the station .S' is shown as comprising a current transformer C, inductance 4' and capacity 5' in all respects-similar to the corresponding elements 0, 4 and 5 at the station S. lVith the switch 3 in the position shown it will be seen that the coil orwinding C is in series with a telephone receiver, orother receiving device, 6' and inductance and capacity 9' and 10 designed for parallel resonance at the frequency of the generator G may be shunted across the receiver 6 for the purpose of shunting out any power frequency current which may pass the anti-resonant set 4', 5'.

' The impedances 7' 8 are preferably so designed or adjusted that the receiving circuit containing the receiver 6' will be tuned to,

or resonant at, the frequency of the gener ator G, whereby a maximum amount of signaling current will flow through the receiver 6 The impedances 7, 8 are also preferably designed or adjusted for series resonance at the signaling frequency. With such design the combined impedance 7 -8 will materially restrict the flovaof any pow er frequency current which may pass the set mean is 4'5'. While we have described a sending means at the station S and receiving means at station S it is preferable, of course, to provide both a sending means and receiving means at each station. \Ve have shown such a system in Fig. 1, the elements K and G at station S corresponding to elements K and G at station S and elements6, 7, 8, 9 and 10 at station S corresponding to elements .6, 7, 8, 9 and 10 at station S. In short the signaling equipment at one station is identical to that at the other.

To understand the operation of the system above described, let it be assumed that the line Z Z Z is carrying current at cycles and that both switches 3, 3 are in the receiving position. If the operator at station S desires to communicate with the operator at the station S the former need only start his generator G through switch 3 to sending osition and then manipulate the key K in tie usual manner. The receiving circuit at S bein tuned to the frequency of the generator the operator at S will be able to read the message by means of the instrument 6'. Due to the shunts 4'5' and 910, as well as the impedance offered to the power current by the element-s 7, 8, the receiver 6 will be free from any noise which would otherwise be caused by the power current. Signalling from station S may be accomplished in a similar manner.

The system above described may be modified in various respects. Thus, instead of relying on the elements 4, 5, 4, 5, 9, 10, 9, and 10' to restrict or substantially eliminate the How of power current in the local signalling circuits, some or all of these elements may be omitted and the arrangement shown in Fig. 2 adopted. In this figure, which depicts the apparatus at one station (the apparatus at the other station being identical), the elements K, G, C, Z, 3, 6, 7 and 8 will at once he recognized in view of the explanaiiq little impedance to the flow of the signalling I current.

Instead of employing a separate generator G, or G for superimposing a signa ling frequency on the power transmission line the arrangement. shown in Fig. 3 may be adapted. To simplify the explanation we have omitted the receiving means at the station former and the power currents are transmitted over the transmission line in the usual and normal manner. -But when the key K is depressed the circuit including winding C is opened and the current, in the other winding (primary) of the current transformer then causes the ferrous magnetic circuit (not shown) of the current transformer to become greatly over-saturated. This introduction of impedance in the power line 1 distorts the shape of the wave of the power current and introduces hi her harmonics into the transmission line. uppose that the freuency of the power current is cycles and t e design of the transmitting means is such that, on depression of the key K, a third harmonic is introduced into the transmission line. The sets 45 and 9--10, should then be tuned to be anti-resonant to a frequency of 3X60 i. e. 180 cycles, and the circuit containing the receiver- 6' should be designed to be resonant at the last mentioned frequency. The receiver 6' will then respond to the third harmonic but will be substantially unaffected by the fundamental of the powercurrent wave. In other words the receiver 6 will respond every time the key K is depressed.-

A still different means for impressing a signalling current of a different frequency upon the line is shown in Fig. 11. Two

transformers 21 and 22 are provided. When the normally open key K is closed current at the power freqligency f is sup lied to the rimaries P and 2 in series. eprimary l has comparatively few turns and the primary 1? many turns so that the iron is magnetized more intensely in 22 than in 21'. The two secondaries S and S areso wound and connected that the E. M. F.s of the fundamental frequenty neutralize each other, but the third harmonics cause a current flow in the coil C at a frequenc 3f. This may be more readily understood y referring to 12 in which the curve 22' represents the M. F. in the secondary S the curve 21 that in secondary S and curve R the resultant triple frequency E. M. F. in the coil C. Any of the three types of receiving circuits shown in Figs. 1, 2 or 3 may be emphiyed with the transmittingmeans shown in ig. 11.

Various modifications in the method of coupling the sending and receiving circuits to powertransmission line may be resorted to. Thus instead of coupling the current transformers C and C to the high tension line they may be coupled to the low tension side as indicated at G in Fi 4. Or, instead of emfploying current trans ormers, potential trans ormers may be employed. Thus in Fig. 5 one winding of the transformer is connected across phase 1-1 on the high tension line, the other winding being indicated at C. A further modification is illustrated in Fig. 6 in which the rimary and secondary of the transformer are Y connected, the transformer C havin one of its windings inserted in the lead which connects the neutral point of the secondary of the transformer to ground.

In Fi 7 we illustrate a further modifica tion in t e manner of coupling the signalling circuits to the power transmission s stem. In thisfigure the primary of the trans ormer is delta connected while the secondary is Y connected. The primary of the transformer T is delta connected as is also the secondar thereof. The signalling set at the station is coupled to the power transmission system by means of a current transformer in one of the low tension phases of the transformer T. The signalling set at the station S is coupled to the power transmission system b means of two current transformers C, one connected in one of low tension phases of the transformers T and the other in another low tension phase of said transformer T. The relative direction of flow of the signalling ma be seen by inspection of Fig. 7 in which t e arrows indicate direction of flow at a particular instant.

The disclosure, up to this point, has been restricted to telegraphic systems, i. e., systems in which the frequency of the signalling current is between 400 and 1000 cycles per second. At least some, if not all of the system thus far described may be utilized, by employment .of pro er sending and re.- ceiving instruments, or telephonic communication. In this case a si alling freuency of-5000 cycles per secon or upwards t ereof, is preferably employed. To avoid unnecessary sur lusage we show but one adaptation of the invention to telephonic communication and in this illustration the receivin set is omitted from one station and the sen ing or transmitti'n set from the other for the sake of simpli cation. Referring to Fig. 8, the simi arit between the most of the elements there s own and the corresponding elements in Fig. 1 will at once be a parent. The generator G, in this case, pre erabl has a f uency of at least 5000 cycles and the key is replaced by a microphone or tele hone transmitter M. It will also be noted that the telephone re Ill Ill

ceiver 6' has connected in series therewith a criysstal detector or other suitable rectifier isdisclosed and claimed in our copending This modification of our invention application, Serial No. 235,430, filed November 25, 1927, which is a division of this application.-

In operation the operator at station S speaks into the device M thus modulating the high frequency current and the sound vibrations will be reproduced at 6 as will be apparent to those skilled in the art in view of the above disclosure.

From the above descriptionof our invention it will be appreciated that we have provided communicating'systems in which the power-conveying conductors alone are employed to convey the signalling current without any substantial interference with the power transmission. No line wires other than the power lines are required so that the installation as well as maintenance costs are minimized. Furthermore, by virtue of the per second) intervals per secon sets 45, 4'5', 9-10 and 9-10' which are designed or adjusted for parallel or anti-resonance at the signalling frequency employed or the sets 1112 designed for parallel resonance at the power frequency; there is practically no noise caused in the receiving instrument by the low frequency power current.

A system specially different but from a generic standpoint in many respects the same as those already described, is illustrated in Fig. 9. Before describing this system in detail, we wish to explain the theory upon which it is based. The curve 30in Fig. 10.represents the power current in the line wire Z It will be noted that this current asses through zero twice in each cycle. 11 other words there are 2f (where f is the power frequenc in cycles in which the line Z is dead and may be employed to convey signalling current. Furthermore, if means are provided to render the signalling circuits operative only when the power current is substantially zero, the last mentioned current will be substantially prevented from flowing to the signalling instruments. One form of means for accomplishing these functions is indicated diagrammatically in Fig. 9. Here again for the sake of simplicity we show only one transmitting means and one receiver. The elements 1 1 C, C and K will at once he recognized. The key K is connected in series with the winding C of the current transformer, a battery 31 and a circuit controller. The last mentioned device comprises one or more contact segments 32 adapted to be engaged by a contact arm 33 mounted on a shaft 34. The shaft 34 is driven by a synchronous motor 35 supplied from the power line by any suitable connections. The design and adjustment of the contacts 32-33 is such that current cannot flow through the said contacts except when the power current in line I is substantially zero and then only if the key K is closed, It will therefore be understood that when the key K is closed unidirectional current impulses will pass through the winding C at a rate of 2f per second, each impulse occurring at a time when the power current is zero. The receiving system shown at S is a duplicate of the system shownat S except that battery 31 and key K are omitted and receiving in-.

strument 6' substituted therefor.

In operation, when the key K is closed the receiver 6 will receive current impulses at the rate of 2f per second and a comparatively loud note of this pitch will beemitted thereby. When the key is open no signaling current is transmitted nd as the contacts 3233 are designe to close only when the E. M. induced in the coil C by the power current is substantially zero, there will be practically no sound in said receiver at this time.

. In Fig. 13 we have illustrated a system in which the set 4, 5 is omitted in the sending circuit, the set 7, 8 being designed or ad]usted for series resonance at the signalling frequency. This arrangement is particularly adapted to the form of the invention in which the transformers C, C are potential transformers. The set 78' and 78"" in the receiving circuit are each designed or adjusted for series resonance at the signalling frequency and the set 45 for parallel resonance at the same frequency.

The operation of this form of the invention will be understood in view of the ex- 1planation in connection with the preceding gures.

It will be understood that the specific physical embodiments herein disclosed are illustrated only diagrammatically and to avoid confusion and surplusage more or less auxiliary apparatus such as manually operable switches, discharge resistances, blocking condensers etc., which may prove desirable in practice, have been omitted. However, with the present disclosure before him a man skilled in the art could make and use the invention. It is to be borne in mind also that while it is at present preferred to employ the various features and elements in the combinations described, some of these may be altered and others omitted and some'of the features of each modification ma be embodied in the others without interfering with the more general results and effects outlined and the invention extends to such use.

What we claim isf 1. signalling system comprising in comblnatlon, a power transmission line adapted to conduct alternating current at a predetermined fundamental frequency, means energized from .said power transmission line for setting up a harmonic of said fundamental frequency in said line at will, receiving means responsive to said harmonic, and means for substantially preventin flow of current at said fundamental %requency throu h the receiving means.

2. combined power and intelligence conveying system comprising in combination, a multi-phase power generator, a step-up transformer whose primary is delta connected to said generator, a ower transmission line to which the secon ary of said transformer is Y-connected, a step-down transformer delta connected to said line and whose secondary is delta connected, a signalling circuit coupled to said power system by means of a current transformer'in one of the low tension phases of one of said two first named transformers, and a signalling circuit coupled to said power system by means of two current transformers each connected in a different one of the low tension phases of the other of said two firstnamed transformers.

3. A combined power and intelligence con coupled to said power system by means of a current transformer in one of the phases of said primary winding, and a'second signaling circuit coupled to said multi-phase trans mission system by means of two current transformers each connected to a different phase of said system.

4. A combined power and intelli nce consystem by means of a current transformer in one of the phases of the primaryof said first mentioned transformer, and a signaling circuit coupled to said power system by means of two current transformers each connected to a different one of the phases of the secondary of said" second mentioned transformer.

In testimony whereof we hereunto aflix our signatures.

MAURICE L. SINDEBAN D. GEORGEN. TIDD. JOSEPH W. MILNOR. 

